1. Field of the Invention
The invention relates to gate valves.
2. Description of the Prior Art
There are many valve installations, for example in subsea wellhead equipment, where metal-to-metal sealing is a requirement and, other things being equal, gate valves would desirably be used as they are easily produced with a metal-to-metal seal and stroking of the valve provides a self-cleaning action when the gate is held in contact with the valve seat. However, in the smaller bore sizes, for example of the order of 12.5 mm bore, the gate valves at present available suffer from serious disadvantages.
One marked disadvantage of small bore gate valves currently available is that they are unduly large for their bore size, usually being sized-down versions of larger, say 50 mm to 150 mm bore, valves. A further disadvantage is that although they theoretically provide metal-to-metal sealing the construction is such that in practice there is a possibility of movement of the valve seats fitted within the valve bodies, which immediately renders suspect the resilient seat to body seals which are employed.